Entourage 2008 does actually have a .plist for Sync Services: ~/Library/Preferences/com.microsoft.entourage.syncservices.plist.
I haven't tried managing it via managed preferences (MCX) in the JSS but looks like it should be possible.
Display Name: Disable Sync Services (calendar)
Apply Setting To: User Level Enforced
Domain: com.microsoft.entourage.syncservices
Key Name: sync calendar
Key Type: boolean
Value: False
You may need to apply this as User Level At Every Login if User Level Enforced doesn't work.
You would also need to make three more managed preference entries for these keys:
- sync contacts
- sync notes
- sync tasks
Kudos to Charles Edge for documenting the settings a few years ago: Disable SyncServices.
